switching FETs or relays

I want to run my amplifier via batteries and use a TTL driven switch to turn it ON, only when it's needed - to save power. So for +/- 12 volts with 20 mA should i go with FETs or just used mechanical switches?

Reply to
MisFat
Loading thread data ...

A couple of MOSFET switches are going to be cheaper, more compact and much less power hungry.

Using a TTL output (switching between 0.4V and around 3.0V) to control a P-channel MOSFET sourcing your +12V and an N-channel MOSFET sourcing your -12V is going to take a little fiddling.

A 1k pull-up resistor from the TTL output to +5V would give you useful extra output swing.

You could use a "logic level" N-MOSFET - gate tied to the TTL output, source tied to 0V and drain tied to the gate of the P-channel MOSFET to control the +12V rail. You will need a resistor (perhaps100k) tied to the +12V supply to make sure that the P-channel MOSFET turns off.

Turning on the -12V rail is a little more difficult. Perhaps the easiest way to do it would to use a second P-channel MOSFET in parallel with the one switching the +12V rail to drive the gate of the N-channel MOSFET driving the -12V rail. Again, you will need a resistor from the drain of the second P-channel MOSFET to the -12V supply to make sure that the N-channel MOSFET is fully off when it is supposed to be off.

Hope this helps.

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

use a hex fet or some logic fet rated for the current and voltage. pick one that has the lowest On Resistance

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
 Click to see the full signature
Reply to
Jamie

On Sep 2, 9:38 pm, " snipped-for-privacy@gmail.com" wrote:

Here you go. This uses a pair of N and P channel mosfets along with some level shifting. It also incorporates current limiting for start up and just in case. Sorry about the limited, lack of, explanation and component values.

Grab hold of LTSpice.....

formatting link

Then cut and paste the text below into Notepad and save the file with an .asc extension. Then you can load it into LTspice to look at it.

Version 4 SHEET 1 880 920 WIRE -208 -224 -256 -224 WIRE -176 -224 -208 -224 WIRE -64 -224 -96 -224 WIRE 0 -224 -64 -224 WIRE 352 -224 96 -224 WIRE -64 -192 -64 -224 WIRE -208 -128 -208 -224 WIRE -112 -128 -208 -128 WIRE 16 -128 16 -176 WIRE 16 -128 -16 -128 WIRE -208 -48 -208 -128 WIRE -192 -48 -208 -48 WIRE 16 -48 16 -128 WIRE 16 -48 -112 -48 WIRE 16 -16 16 -48 WIRE 16 96 16 64 WIRE 112 144 80 144 WIRE 160 144 112 144 WIRE 288 144 240 144 WIRE 416 144 352 144 WIRE 112 176 112 144 WIRE 16 240 16 192 WIRE 112 288 112 256 WIRE 112 288 80 288 WIRE 352 288 352 160 WIRE 352 288 112 288 WIRE 352 320 352 288 WIRE 16 368 16 336 WIRE -192 480 -224 480 WIRE 16 480 16 448 WIRE 16 480 -112 480 WIRE -224 560 -224 480 WIRE -112 560 -224 560 WIRE 16 560 16 480 WIRE 16 560 -16 560 WIRE 16 608 16 560 WIRE -224 656 -224 560 WIRE -224 656 -256 656 WIRE -192 656 -224 656 WIRE -64 656 -64 624 WIRE -64 656 -112 656 WIRE 0 656 -64 656 WIRE 352 656 96 656 FLAG 352 320 0 FLAG 416 144 CTRL IOPIN 416 144 In FLAG -256 -224 +12 IOPIN -256 -224 In FLAG -256 656 -12 IOPIN -256 656 In FLAG 352 -224 +12S IOPIN 352 -224 Out FLAG 352 656 -12S IOPIN 352 656 Out SYMBOL pmos 96 -176 M270 WINDOW 0 98 83 VLeft 0 WINDOW 3 74 83 VLeft 0 SYMATTR InstName M1 SYMBOL nmos 96 608 R90 WINDOW 0 71 47 VRight 0 WINDOW 3 95 10 VRight 0 SYMATTR InstName M2 SYMBOL npn 80 96 M0 WINDOW 0 79 36 Left 0 WINDOW 3 61 60 Left 0 SYMATTR InstName Q1 SYMBOL pnp 80 336 R180 WINDOW 0 83 60 Left 0 WINDOW 3 70 34 Left 0 SYMATTR InstName Q2 SYMBOL Digital\\\\buf1 352 80 M0 SYMATTR InstName TTL SYMBOL res -208 -32 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 10K SYMBOL res -96 464 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 10K SYMBOL res 96 160 R0 WINDOW 0 38 50 Left 0 SYMATTR InstName R3 SYMATTR Value 2K2 SYMBOL res 256 128 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 4K7 SYMBOL res -80 -240 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R5 SYMATTR Value 6R8 SYMBOL res -96 640 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R6 SYMATTR Value 6R8 SYMBOL pnp -16 -192 R90 WINDOW 0 83 42 VRight 0 WINDOW 3 108 26 VRight 0 SYMATTR InstName Q3 SYMBOL npn -16 624 M270 WINDOW 0 104 72 VLeft 0 WINDOW 3 79 70 VLeft 0 SYMATTR InstName Q4 SYMBOL res 0 -32 R0 WINDOW 0 36 51 Left 0 SYMATTR InstName R7 SYMATTR Value 4K7 SYMBOL res 0 352 R0 WINDOW 0 40 50 Left 0 SYMATTR InstName R8 SYMATTR Value 4K7

Reply to
Genome

On Sep 2, 9:38 pm, " snipped-for-privacy@gmail.com" wrote:

This one has some more meaningful values on it and you get to run an analysis.

Version 4 SHEET 1 988 920 WIRE -224 -240 -272 -240 WIRE -176 -240 -224 -240 WIRE -64 -240 -96 -240 WIRE 0 -240 -64 -240 WIRE 672 -240 96 -240 WIRE 752 -240 672 -240 WIRE 864 -240 752 -240 WIRE -64 -208 -64 -240 WIRE -224 -144 -224 -240 WIRE -112 -144 -224 -144 WIRE 16 -144 16 -192 WIRE 16 -144 -16 -144 WIRE -224 -64 -224 -144 WIRE -192 -64 -224 -64 WIRE 16 -64 16 -144 WIRE 16 -64 -112 -64 WIRE 16 -32 16 -64 WIRE 672 -16 672 -240 WIRE 752 -16 752 -240 WIRE -224 80 -224 -64 WIRE 16 80 16 48 WIRE 112 128 80 128 WIRE 160 128 112 128 WIRE 288 128 240 128 WIRE 464 128 352 128 WIRE 560 128 464 128 WIRE 112 176 112 128 WIRE 464 176 464 128 WIRE -224 208 -224 160 WIRE -224 208 -256 208 WIRE -256 240 -256 208 WIRE 16 240 16 176 WIRE -224 256 -224 208 WIRE 112 288 112 256 WIRE 112 288 80 288 WIRE 352 288 352 144 WIRE 352 288 112 288 WIRE 464 288 464 256 WIRE 464 288 352 288 WIRE 672 288 672 48 WIRE 672 288 464 288 WIRE 752 288 752 64 WIRE 752 288 672 288 WIRE 464 320 464 288 WIRE 16 368 16 336 WIRE -224 480 -224 336 WIRE -192 480 -224 480 WIRE 16 480 16 448 WIRE 16 480 -112 480 WIRE 752 512 752 288 WIRE 672 528 672 288 WIRE -224 560 -224 480 WIRE -112 560 -224 560 WIRE 16 560 16 480 WIRE 16 560 -16 560 WIRE 16 608 16 560 WIRE -224 656 -224 560 WIRE -224 656 -256 656 WIRE -192 656 -224 656 WIRE -64 656 -64 624 WIRE -64 656 -112 656 WIRE 0 656 -64 656 WIRE 672 656 672 592 WIRE 672 656 96 656 WIRE 752 656 752 592 WIRE 752 656 672 656 WIRE 848 656 752 656 FLAG 464 320 0 FLAG 560 128 CTRL IOPIN 560 128 In FLAG -272 -240 +12 IOPIN -272 -240 In FLAG -256 656 -12 IOPIN -256 656 In FLAG 864 -240 +12S IOPIN 864 -240 Out FLAG 848 656 -12S IOPIN 848 656 Out FLAG -256 240 0 SYMBOL pmos 96 -192 M270 WINDOW 0 98 83 VLeft 0 WINDOW 3 74 83 VLeft 0 SYMATTR InstName M1 SYMATTR Value BSS84 SYMBOL nmos 96 608 R90 WINDOW 0 71 47 VRight 0 WINDOW 3 95 -1 VRight 0 SYMATTR InstName M2 SYMATTR Value BSS123 SYMBOL npn 80 80 M0 WINDOW 0 107 36 Left 0 WINDOW 3 61 60 Left 0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL pnp 80 336 R180 WINDOW 0 101 60 Left 0 WINDOW 3 57 34 Left 0 SYMATTR InstName Q2 SYMATTR Value 2N3906 SYMBOL Digital\\\\buf1 352 64 M0 SYMATTR InstName TTL SYMATTR SpiceLine Vhigh=3D5V Vlow=3D0V Trise=3D100n Tfall=3D100n SYMBOL res -208 -48 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 100K SYMBOL res -96 464 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 100K SYMBOL res 96 160 R0 WINDOW 0 38 50 Left 0 SYMATTR InstName R3 SYMATTR Value 47K SYMBOL res 256 112 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 47K SYMBOL res -80 -256 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R5 SYMATTR Value 6R8 SYMBOL res -96 640 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R6 SYMATTR Value 6R8 SYMBOL pnp -16 -208 R90 WINDOW 0 76 48 VRight 0 WINDOW 3 100 1 VRight 0 SYMATTR InstName Q3 SYMATTR Value 2N3906 SYMBOL npn -16 624 M270 WINDOW 0 104 81 VLeft 0 WINDOW 3 79 82 VLeft 0 SYMATTR InstName Q4 SYMATTR Value 2N3904 SYMBOL res 0 -48 R0 WINDOW 0 36 51 Left 0 SYMATTR InstName R7 SYMATTR Value 47K SYMBOL res 0 352 R0 WINDOW 0 40 50 Left 0 SYMATTR InstName R8 SYMATTR Value 47K SYMBOL cap 656 -16 R0 WINDOW 0 -59 28 Left 0 WINDOW 3 -61 52 Left 0 SYMATTR InstName C1 SYMATTR Value 100=B5 SYMBOL cap 656 528 R0 WINDOW 0 -58 16 Left 0 WINDOW 3 -60 40 Left 0 SYMATTR InstName C2 SYMATTR Value 100=B5 SYMBOL voltage 464 160 R0 WINDOW 0 43 56 Left 0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value PULSE(0 5 1 100n 100n 1 2) SYMBOL res 736 -32 R0 WINDOW 0 39 43 Left 0 WINDOW 3 39 69 Left 0 SYMATTR InstName R9 SYMATTR Value 220R SYMBOL res 736 496 R0 WINDOW 0 36 53 Left 0 SYMATTR InstName R10 SYMATTR Value 220R SYMBOL voltage -224 64 R0 WINDOW 0 36 46 Left 0 WINDOW 3 35 70 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12V SYMBOL voltage -224 240 R0 WINDOW 0 37 45 Left 0 WINDOW 3 38 70 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value 12V TEXT 112 320 Left 0 !.tran 0 10 0

Reply to
Genome

Very nice...

Reply to
Fred Bloggs

Great, this does make sense. I Appreciate that Genome. Thank you

Reply to
MisFat

:-)

Reply to
Genome

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.